The present invention relates to an arrangement in the headbox of a paper or cardboard machine as defined in the preamble of claim 1, said headbox comprising a pulp suspension feed system that distributes the suspension over the width of the headbox, at least one first flow resistance element, such as a perforated plate and/or tube system provided with flow apertures, from which headbox the pulp suspension is passed via at least one chamber, such as an equalizing chamber and/or the slice gap of a slice chamber, onto a forming wire or equivalent.
The invention concerns the headbox, most appropriately a hydraulic headbox of a paper or cardboard machine. The invention relates to modification of the internal flow within the headbox.
There are prior-art solutions in headboxes, preferably hydraulic ones, that comprise two successive tube systems used to influence the pulp flow in the headbox, e.g. by creating turbulence. At present, in the last tube system in the direction of pulp flow, the tail end of the so-called turbulence generator as seen in the direction of flow is so shaped that it properly fills the lip channel of the headbox, the purpose of which is to establish an even flow in the transverse direction of the machine.
The prior-art tube and tube system are very difficult and expensive to manufacture. In addition, it would be most advantageous to design the shape and size of the tubes according to the flow quantity, which leads to a very expensive structural solution.
Another device used in headboxes are guide plates, also called as trailing plates, baleen plates, or lamellas, which start from the end of the forming tubes and extend in the slice chamber to a point near the headbox lips. The purpose of these plates is to bring a turbulent flow in separation from the other rows to the lip, thus maintaining a high turbulence level. The trailing plates, baleen plates or lamellas are used as a means of correcting the wrongly sized forming tubes at the tail end of the tube system. A solution of this type is disclosed in U.S. Pat. No. 3,607,625.
In another prior-art solution, a system of baffle plates extending over a substantial part of the length of the equalizing chamber is arranged on the exit side of the first tube system, i.e. flow resistance, as seen in the direction of pulp flow. The two opposite surfaces of the baffle plates consist of continuous surface structure in the transverse direction over the entire width of the headbox, without any substantial discontinuities, the baffle plates being thus arranged to balance the pulp flow partly via the pressure loss occurring as the pulp flow relatively suddenly expands at the edge of the baffle plate. A solution of this type is disclosed in patent specification FI 93874 B.
The object of the present invention is to create a completely new type of solution that will obviate the drawbacks of prior art and to achieve a new type of solution for controlling fiber orientation and formation. Another object is to produce a solution that is more advantageous in respect of manufacturing technology for the above-mentioned purpose.